"COLLABORATIVE RESEARCH: Identifying Environmental Determinants Favorable for the Presence and Transmission of Pathogenic Vibrios"
Bacteria classified by scientists as Vibrio are very common in the ocean and some are capable of causing disease in humans. The three major causes of disease are Vibrio cholerae, V. parahaemolyticus and V. vulnificus. Cholera and the so-called non-cholera diseases or vibrioses are reportable to the Centers for Disease Control and Prevention (CDC). All three of these vibrios cause gastroenteritis and wound infections, and in the U.S. the most common agent of disease is V. parahaemolyticus whereas the most lethal is V. vulnificus. Very little is known about the environmental factors that determine the abundance and distribution of these vibrios in their natural environments where they come in contact with humans as a result of swimming or eating undercooked seafood. This research will use the tools of modern molecular biology and chemical oceanography to determine the environmental drivers of vibrio abundance and distribution. Specifically, this project will measure vibrio levels in water, bottom sediment, and oysters in three ecologically and geographically distinct locations ? Chesapeake Bay, Gulf of Mexico and Puget Sound. These data will be correlated with plankton densities and with the following environmental determinants: sea surface temperature, chlorophyll, turbidity, salinity, dissolved organic carbon, primary productivity, particulate organic carbon and nitrogen, dissolved inorganic nutrients, and suspended particulate matter. By linking the in situ measurements with remote sensing imagery, it will be possible to more accurately describe these relationships when real-time environmental sampling is not possible. In addition, this project will host an annual Summer Research Institute to train eight high school students per year in laboratory settings. It is expected that this research will result in a more accurate description of the environmental determinants that influence vibrio abundance and distribution.
Vibrios are naturally occurring bacteria in both fresh water and marine environments. Many Vibrio species are harmless but some can cause a mild to severe infection in humans, the most serious of which is cholera. Since Vibrio species are naturally occurring in the environment, they cannot be eradicated, but protection against infection clearly is possible. The causative agent of cholera is Vibrio cholerae serotype O1, and it is transmitted by contaminated food or drinking water. However, cholera is not an immediate threat in the US because most people have access to safe potable water. Except for a very few cases of cholera that have occurred in the US, most of the cholera cases reported in the US were travelers returning from other countries where cholera is endemic. Vibrio parahaemolyticus is the leading cause of bacterial enteric disease in the US and typically is associated with consumption of raw or undercooked seafood. Despite extensive knowledge of the occurrence and pathogenicity of V. parahaemolyticus, the burden of V. parahaemolyticus related illness remains high and, in fact, the incidence of infections with V. parahaemolyticus in the U.S. has risen since 2000. V. vulnificus, another pathogenic Vibrio species also causes diarrhea, vomiting, and abdominal pain and is transmitted by contaminated seafood. But especially for immunocompromised or immunosuppressed persons, particularly those with chronic liver disease, V. vulnificus is a very serious threat and can cause systemic infection if the bacterium enters an open wound and the infection can result in a severe and life-threatening illness characterized by fever and chills. Fatality can be as high as 50%. Because these pathogens exist naturally in the environment, to protect against the disease, contact with contaminated water should be avoided. During the warmer months of the year, the concentration of vibrios in estuaries and coastal waters tends to be high and direct contact should be avoided if an individual has an abrasion or open wound. Also, care should be taken when handling and eating raw seafood. Elevated water temperature is a predictor of vibrio populations in estuaries but the precise contribution of temperature alone and the relative contribution of temperature, with respect to other factors, namely salinity and nutrients such as dissolved organic carbon, suspended particulate matter, and chlorophyll, have been studied. In our investigation, we observed that all of these parameters can be correlated with abundance of vibrios. For example, temperature accounted for 11 to 14% of the abundance of at least one of the four Vibrio species. The number of Vibrio parahaemolyticus carrying genes for virulence, such as thermostable direct hemolysin (tdh) and tdh-related hemolysin (trh) was determined and similar analyses for V. vulnificus were done. With the combination of environmental parameters correlated with Vibrio species abundance, it is now possible to predict those environmental conditions favorable for growth and multiplication of vibrios that will pose a danger to public health. We will continue to gather data for many countries of the world, especially those where cholera is endemic, to develop a global predictive model to predict risk to public health and provide warning so that health officials can take action to protect the public. In this project, we measured the population sizes of Vibrio species at two sites in Maryland. Water, oyster, and sediment samples were analyzed. Our observations show that potentially pathogenic V. parahaemolyticus is highly variable in distribution and incidence at each locality. Approximately 1.2% of all the culturable V. parahaemolyticus isolates were pathogenic, while approximately 50% of the water samples and approximately 20% of the oyster samples contained V. parahaemolyticus with pathogenic markers, when tested by real-time PCR. Thus nonculturable pathogenic V. parahaemolyticus must be considered to be common in the Chesapeake Bay, warranting seafood monitoring using appropriate methods to minimize risk of disease. More than fifty-five genotypes of V. cholerae carrying up to 12 different virulence factors were also detected, confirming the presence of potentially pathogenic V. cholerae non-O1/non-O139 in the Chesapeake Bay. The majority of the V. vulnificus isolates were from water samples and a few from oysters. Resistance to ampicillin and penicillin was common. Ampicillin resistant V. vulnificus also showed resistance to ß lactams, including aztreonam, ceftazidime, ceftriaxone, cefotaxime, and cefoxitin. All ampicillin resistant strains of V. vulnificus were sensitive to cefepime (FEP). The extensive data collected during this study are continuing to be analyzed and manuscripts are being prepared for publication, all of which will contribute to the understanding of how vibrios interact with the environment. Future studies will build upon these findings, with the hope that the new knowledge can be used to prevent vibrio outbreaks and save lives.
